I turned the corner and there it was. A small bright thing on the ground caught my eye. Normally I would have assumed it to have been thrown away, something of little value. But it had the yellow glint of gold. I paused, hesitating to pick it up. It was a golden key. I bent down to it. It was an old-fashioned type of key with an oval top and a long stem.

I picked it up. It was not a toy, but seemed to be made of old brass and to have been recently polished, although traces of black and verdigris lingered in the engraving. On it was inscribed in copperplate ‘No. 13’.

It felt strangely heavy as I held it in my hand and looked around me. Where could it have come from? I was standing at the intersection of two streets with shops in every direction. Then across the road I saw an extra door between two shopfronts that I had never noticed before: a door painted in glossy black with a brass letterbox and the number 13 in brass above it. I went across the road. The brass escutcheon at the keyhole seemed a good match for the key.

I knocked at the door but there was no reply. But when I stood back and looked up I could see the light was on. A shadow moved behind the net curtain. I knocked again and shouted up:

‘I think you’ve lost your key.’

There was no answer. I wondered about putting it through the letterbox – but what if it was the wrong door? I put the key in the lock and it opened the door. It was dark inside. I fumbled for a light switch and saw the stairs in front of me going straight up. Something warned me not to continue, but I climbed the stairs anyway.

There was silence, no sign of the light and movement that I had seen from outside. On the first floor landing the bulb had no lampshade and cast a harsh shadow beneath my hand, which shook as I held the banister.

Three doors were there, all closed, one either side and one ahead.

’Hello?’ I cleared my throat and tried louder. ‘I think I found your key.’

I knocked on each of the doors in turn, then tried them. Two were locked. The door in front of me opened into darkness.

‘Hello?’

I tried again, but there was no reply. I stepped in, feeling for the light switch, and too late realised that there was empty space where the floor should have been. I fell into the darkness, through space and time, from one world to the next, with the evil spirits of that place laughing with bared and savage teeth.

And so the police were called, when it was realised that I had disappeared. From behind the net curtain I stared out across the road where the squad car had parked. I read the letters on its roof.

A woman in a high-vis jacket got out of the car. She stopped and looked down at the ground. She bent down and picked something up. It was small and bright and as she studied it she glanced across, noticing perhaps the black door and the brass number 13.